This invention relates to the field of toxic waste treatment, and, more particularly to a toxic waste fixant for preventing the leaching of organic and inorganic toxics at unacceptable levels from materials such as soils, sediments, and sludges and cause a significant reduction in the inherent toxicity concentration of a contaminated material by chemical mechanisms as well as a method for using that fixant.
The problem of the safe disposal of toxic waste materials is a pressing one. With the ever increasing generation of hazardous materials in our industrial society, there is a growing demand for strict controls of the handling and disposal of all forms of toxic waste. In response to that demand, legislatures, both state and federal, have passed laws limiting the amount and nature of wastes which may be discharged into the environment. There has been a great deal of movement of late to make these laws more stringent, and reaching the goals set forth in the laws may soon become much more difficult.
Toxic wastes are legally defined in the various statutes and regulations dealing with their handling and treatment, but they may be broadly defined as any material generated as a by-product of an industrial process capable of having an adverse impact upon the environment if discharged without treatment.
The statutes and regulations also set forth the standards to be met by the industry which generates the waste, generally by setting maximum limits of a specified number of parts-per-million (ppm), parts per billion (ppb), or parts per trillion (ppt) of the free waste found in the test samples, as measured relative to a leaching test standard. It is thus the goal of toxic waste treatment processes to reduce the levels of the waste present and or leaching in an excessive degree in the test samples to the lowest levels possible, at least to a level below the mandated maximum.
Known methods of treating toxic wastes, in terms of stabilization/solidification or chemical fixation methods, include, for example the five broad categories of: sorption, lime-fly-ash pozzolan process, pozzolan-Portland cement systems, thermoplastic microencapsulation, and macroencapsulation.
Sorption involves adding a solid to material containing the waste to be treated. The solid soaks up any liquid present, and may produce a soil-like material containing the waste, and is most suitable for applications involving the treatment of non-reactive, non-biodegradable wastes. Typical solids suitable for use in sorption include activated carbon, anhydrous sodium silicate, various forms of gypsum, celite, clays, expanded mica, zeolites, coal fly ash, cement kiln dust, and lime.
Lime-fly-ash pozzolanic processes utilize a finely divided, non-crystalline silica in fly ash, and the calcium in the lime to produce a low-strength cementation. The treated wastes are entrapped within the pozzolan concrete matrix (micro-encapsulation), thereby removing them from contact with the environment.
Pozzolan-Portland systems use Portland cement and fly ash, or other pozzolan materials to produce a stronger type of waste/concrete composite. Waste containment results from microencapsulation of the waste in the concrete matrix. Soluble silicates may be added to accelerate hardening and metal containment.
Thermoplastic microencapsulation involves blending fine particulate waste with melted asphalt or other matrix. Liquid and volatile phases associated with the wastes are isolated in a mass of cooled, hardened, asphalt. The resultant material can be buried without a container.
Microencapsulation systems contain waste by isolating large masses of the waste using some form of jacketing material. The most carefully researched systems use a 208-drum or polyethylene jacket fused over a monolithic block of solidified wastes.
These systems are useful, and appropriate for many applications, but they are not suitable for meeting all current state and federal laws and for all types of materials. There still exists a need for a solidification/stabilization/fixation system for treating toxic wastes to prevent the leaching of impermissible levels of these organic and inorganic wastes into the environment, particularly soils, sediments, and sludges that contain relatively high levels of organics as well as inorganic toxic constituents. There thus exists a need for a new material which can be used in certain applications for the disposal or containment of some of these forms of toxic wastes to a greater degree than heretofore known.